1. Technical Field
The disclosure relates in general to a power detector, and more particularly to a zero bias power detector.
2. Description of the Related Art
The power detector is an energy sensing element which is crucial to a wireless communication system and is most commonly used in a power amplifier. The power detector couples the power emitted from the output terminal of a power amplifier, and further feedbacks the power to the backend processor for monitoring and adjustment. Thus, the connection between the power amplifier and the base station is adapted according to the intensity and distance of the signal to assure that the maximum allowable transmission power is not exceeded and stable system efficiency is maintained.
Conventionally, the power detector can be divided into the zero bias power detector and the active type power detector. The zero bias power detector does not need to be biased, but the active type power detector needs to be biased. Referring to FIG. 1, a circuit diagram of a conventional zero bias power detector is shown. FIG. 1 shows a conventional zero bias power detector 40 disclosed in U.S. Pat. No. 3,647,845B1. The conventional zero bias power detector 40 couples the RF signal to a diode 74 through a capacitor 70 at the input terminal, and outputs a DC voltage according to the transduction capacity of the power of the diode 74 with respect to the current. The capacitor 100 pF, such as a low-pass filter, blocks the time-varying current component so that the output current contains the DC component only. The diode 74 is operated in a zero bias state without using any extra DC voltage, and the rectifying efficiency is dependent on the manufacturing process of the diode 74.